Known switching devices used in electrical circuits, such as in low or medium voltage electric circuits, such as circuit breakers, disconnectors and contactors, which are devices designed to allow the correct operation of specific parts of the electric circuits in which they are installed, and of the associated electric loads. For purposes of the present disclosure, the term “low voltage” is referred to applications with operating voltages up to 1000V AC/1500V DC and the term “medium voltage” is referred to applications in the range from 1 kV to some tens of kV, e.g. 50 kV.
The switching devices include one or more electrical poles, or phases, each having at least a movable contact and a corresponding fixed contact. An operating mechanism is operatively associated to the movable contacts to cause the movement of such contacts between a first closed position in which they are mechanically coupled to the corresponding fixed contacts (e.g., closed switching device) and a second open position in which they are spaced away from the corresponding fixed contacts (e.g., open switching device).
Mechanically operated switching devices include an operating mechanism of the “stored-energy” type, e.g., an operating mechanism having elastic means, such as a pair of springs, which are compressed to store the energy specified for displacing the movable contacts from the closed position to the open position.
Several shunt releases and/or accessories can be operatively associated to the stored-energy operating mechanism; use of such shunt releases and/or accessories is to release or lock one or more mechanical parts of the associated operating mechanism. For example, shunt opening releases can be arranged to act on the operating mechanism to cause the release of its compressed elastic means, following an open or trip command.
FIG. 1 illustrates a mechanically operated tri-polar switching device 500 of a known implementation. The switching device 500 has an operating mechanism 10 operatively connected to the three movable contacts 3 of the poles 2 to cause the coupling/separation of such contacts 3 to/from the corresponding fixed contacts The operating mechanism 10 can include, for example, a pair of springs 11 to provide the energy specified to open the switching device 500.
The known switching device 500 of FIG. 1 includes: an opening shunt release 5 configured for causing the opening of the switching device 500 upon receiving a shunt trip command; an under-voltage shunt release 6 configured for causing the opening of the switching device 500 and/or locking the opened switching device 500 upon the detection of an under-voltage condition; a closure shunt release 7 configured for causing the closure of the switching device 500 upon receiving a closure command; and a locking magnet 8 which is configured to lock the operating mechanism 10 and block the closure of the switching device 500.
Further, a redundant opening shunt release may be provided, having substantially the same functionalities of the opening shunt release 5.
The shunt opening release 5 and the under-voltage shunt release 6 each includes an electrical winding operatively associated to an armature movable between a first attracted position and a second released position, wherein the movement from the attracted to the released position causes the intervention of the armature on one or more parts of the operating mechanism 10 to open the switching device 500.
The shunt trip command can cause the application of power supply to the winding of the opening shunt release 5, to generate a magnetic force moving the armature from the retracted position the released position.
The armature of the under-voltage shunt release 6 in the retracted position compresses a spring and it is held in such retracted position by a magnetic force generated by continuously energizing the winding with an auxiliary power supply. Because of the under-voltage condition occurrence, the auxiliary power supply at least reduces in such a way that the compressed spring releases and urges the armature towards the released position.
One or more additional accessories 80, 9 may be associated with the under-voltage shunt release 6. For example, some applications of the switching device 500 specify a delay time between the occurrence of an under-voltage condition and the consequent intervention of the under-voltage shunt release 6 to open the switching device 500. The energy specified to hold the armature of the under-voltage shunt release 6 in the retracted position during the delay time is provided by means of one or more external capacitors 9, which are for example connected between the auxiliary power supply and the winding of the under-voltage shunt release 6.
Further, in some applications of the switching device 500 can be called on to provisionally disable the opening and/or locking functionality of the under-voltage shunt release 6 upon the occurrence of an under-voltage condition. A mechanical override device 80 can be operatively coupled to the under-voltage release 6 to mechanically block, when activated by an operator, the armature of the undervoltage release 6 in the retracted position, even if an under-voltage condition has occurred.
At the current state of the art, although known solutions perform in a rather satisfying way, there is still reason and desire for further improvements.